1. Field of the Invention
The present invention relates to a printing element substrate, a liquid ejection head, and an inkjet printing apparatus, and, in particular, to the configuration of a liquid supply hole that is provided in a substrate of a liquid ejection head that ejects a liquid such as ink.
2. Description of the Related Art
A liquid ejection head such as a printing head that is used in an inkjet printing apparatus, for supplying a liquid to liquid ejection portions that are provided on one side of a substrate, adopts a system in which a through hole (liquid supply hole or liquid supply passage) is provided in the substrate to supply the liquid from the opposite surface of the substrate, for example. Japanese Patent Laid-Open No. 2007-269016 describes the configuration of the liquid supply hole provided in the substrate of the liquid ejection head, in which a sectional area of the liquid supply hole increases in the supply direction of the liquid and after that, decreases. This configuration will hereinafter be also referred to as “rhomboid configuration”. Since the liquid supply hole is formed in the rhomboid configuration, a size of the printing element substrate, particularly a size in the width direction can be made small to downsize the liquid ejection head or it is possible to suppress the liquid ejection head from being large in size due to an increase in kind of the liquid.
On the other hand, however, in a case of the liquid ejection head having a rhomboid supply passage configuration, there occurs a problem that air bubbles generated in the liquid tend to be easily accumulated in this rhomboid section, and thereby flow of the liquid to be supplied is interrupted to cause an ejection failure in the liquid ejection head. To deal with this problem, Japanese Patent Laid-Open No. 2000-177119 describes a method for making air bubbles retained in an end region away from an ink supply hole to avoid an ejection failure. In addition, Japanese Patent Laid-Open No. H04-250046(1992) describes the construction in which a sectional configuration of an ink supply hole is formed on a polygonal shape such as a rectangular shape or a groove is formed in the periphery of the ink supply hole, thus ensuring liquid flow in the liquid supply passage with the corners or the groove even when air bubbles are retained in the liquid supply passage.
However, in a case of adopting the method for providing the air bubble retention area to suppress the ejection failure as described in Japanese Patent Laid-Open No. 2000-177119, the suppression effect can be expected in a case where a size of the air bubble is small, but in a case where a relatively large air bubble is retained in the liquid supply hole, even when the air bubble is introduced to the retention area, in some cases apart of the air bubble possibly interrupts the flow of the liquid.
In many cases a sectional configuration of the liquid supply passage in a direction perpendicular to the liquid supply direction is rectangular as described in (FIG. 1 of) Japanese Patent Laid-Open No. 2007-269016. In this case, even when the air bubble is retained in the supply hole, the liquid flow in the flow passage can be ensured by the corner section of the rectangular shape as described in Japanese Patent Laid-Open No. H04-250046 (1992). However, in a case where the air bubble is retained to be closer to one side of the rectangular shape and therefore do not close the entire cross section, there are some cases where there occurs a difference in flow speed between the section not closed and the corner section at the time of supplying the liquid. The difference in flow speed causes the air bubble to move to the liquid ejection portion side, from which a problem of closing an inlet of the ejection portion is derived, for example.